PREN Calculator

Calculate the Pitting Resistance Equivalent Number (PREN) to evaluate the corrosion resistance of stainless steels and alloys, especially in chloride environments (e.g., seawater, chemical processing).

PREN
Calculator

PREN = %Cr + 3.3×(%Mo + 0.5×%W) + 16×%N
Cr%
Mo%
W%
N%
PREN: 0
Enter alloy composition values
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Quick Answer

👉 PREN indicates resistance to pitting corrosion:

  • Higher PREN = Better corrosion resistance

✔ Typical ranges:

Material Type PREN Value
304 Stainless ~18–20
316 Stainless ~23–28
Duplex Stainless ~30–40
Super Duplex >40

Formula (PREN Calculation)

The PREN formula considers alloying elements that improve corrosion resistance:

  • Chromium (Cr) → base corrosion resistance
  • Molybdenum (Mo) → pitting resistance
  • Tungsten (W) → enhances Mo effect
  • Nitrogen (N) → significantly boosts resistance

👉 See formula above for exact calculation.

Example Calculation

Given:

  • Cr = 18%
  • Mo = 2.5%
  • W = 0%
  • N = 0.1%

👉 PREN =
18 + 3.3 × (2.5 + 0) + 16 × 0.1
= 18 + 8.25 + 1.6
= 27.85

✔ Equivalent to 316 stainless steel performance

How to Use This Calculator

  1. Enter Chromium (Cr %)
  2. Enter Molybdenum (Mo %)
  3. Enter Tungsten (W %) (optional, default = 0)
  4. Enter Nitrogen (N %)
  5. Instantly get PREN value

✔ Real-time calculation
✔ Ideal for material selection

Common Engineering Uses

1. Material Selection for Corrosive Environments

  • Compare stainless steels for seawater or chemical exposure

2. Offshore & Marine Engineering

  • Ensure adequate resistance to chloride attack

3. Chemical Processing Equipment

  • Select alloys for aggressive environments

4. Stainless Steel Comparison

  • Benchmark grades like 304 vs 316 vs duplex

Typical PREN Values (Reference)

Material PREN
304 Stainless Steel ~18–20
316 Stainless Steel ~24–28
2205 Duplex ~34–36
2507 Super Duplex ~40–45+

Important Notes

  • PREN is an empirical indicator, not an absolute guarantee
  • Does not account for:
    • Surface finish
    • Welding effects
    • Temperature or stress corrosion

👉 Always validate with real-world testing for critical applications.

Related Tools

  • Material Grade Finder
  • Alloy Comparison Tool
  • Density Calculator
  • Surface Finish Calculator

FAQ

What is PREN?

PREN stands for Pitting Resistance Equivalent Number, used to estimate corrosion resistance.

Why is nitrogen important?

Nitrogen has a strong positive effect on pitting resistance.

Is higher PREN always better?

Yes for corrosion resistance, but may increase cost and machining difficulty.

Can PREN replace corrosion testing?

No, it is only a guideline, not a substitute for testing.

Which material has the highest PREN?

👉 Super duplex stainless steels typically have the highest values.

CNC Machining Shops

CNC Machining Shops

Need Corrosion-Resistant CNC Machined Parts?

Selecting the right alloy ensures long-term performance.

👉 We offer:

  • CNC machining for stainless steels and super alloys
  • Material selection support for corrosive environments
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Upload your CAD file today and get a corrosion-resistant solution.